German patent publication 33 08 080 discloses a procedure wherein a relationship is pregiven between the tire pressure, which is present in a vehicle tire, and the vehicle road speed. For the particular value of the tire pressure, a reliable value for the vehicle road speed is selected from the pregiven relationship. If the permissible road speed is exceeded, then the driver is informed by an optical and/or acoustical signal and/or, in one embodiment, an intervention is undertaken via a road speed control electronic system. This intervention reduces the vehicle speed to the permissible value.
In the known solution, it is not considered that a tire having a lower pressure can have a reduced service life compared to a tire with the prescribed air pressure. This applies also for so-called xe2x80x9crun flatsxe2x80x9d, that is, those flats which can, inter alia, be driven without air pressure.
In the state of the art, there are many solutions for detecting a loss of tire pressure. It is known to measure the tire pressure directly. Furthermore, solutions are known wherein a direct measurement of the tire pressure is not made and a tire pressure loss is determined, for example, on the basis of wheel speed signals. In this connection, reference can be made to U.S. Pat. No. 5,712,616, incorporated herein by reference.
The known solutions do not consider that a tire having a lower pressure has a reduced service life compared to a tire with prescribed air pressure.
It is an object of the invention to provide a method for controlling a motor vehicle when there is a loss of tire pressure.
The method of the invention is for controlling a vehicle when there is a loss of tire pressure. The method includes the steps of: detecting if a pressure loss has occurred in at least one tire; and, if a pressure loss in at least one tire is detected, then limiting the speed of the vehicle to a limit value dependent upon at least one of the distance traveled and the elapsed operating time since occurrence of the fault.
By determining the maximum distance range, which can still be traveled with a tire having a reduced air pressure, the reduced service life of a flat tire or a tire having a low air is pressure is considered in the control of the vehicle. The determination of the range in dependence upon the vehicle speed is advantageous.
It is especially advantageous that an automatic limiting of the distance range takes place in dependence upon the actual road speed whereby the driver of the vehicle is compelled to change the tire or to add air thereto. In this way, the general further travel of the vehicle with reduced tire pressure or with a flat is substantially limited so that an increased safety is achieved also for other traffic participants.
As an alternative or supplement to limiting the distance range or range, it is especially advantageous to indicate the maximum range or the distance still remaining, for example, via the on-board computer. In this way, the driver is enabled to optimize the speed of the vehicle at reduced tire pressure.
In an especially advantageous manner, a known function is utilized for the detection of a tire pressure loss which avoids a complex sensor system and especially a direct measurement of the tire pressure.
It is further advantageous that the road speed is limited when tire pressure loss is detected. A limiting of the range additionally takes place which is dependent upon the actual speed of the vehicle. For limiting the range, the speed of the vehicle is steadily reduced to lower values if a distance was traveled since the occurrence of the pressure loss (which distance corresponds to a limit range) until, when reaching the maximum range, the speed has reached the value 0 or a very low value which permits reaching the next service station.
In an especially advantageous manner, the driver has complete control and responsibility for the vehicle even for a tire pressure loss below the limit speed.
In the context of the foregoing and following description, the term xe2x80x9ctire pressure lossxe2x80x9d corresponds to any operating situation for which the air pressure in a tire drops below a minimum pressure and this is independent of the nature of the reduction or of the cause, et cetera.